Compensation for deficient charge roll in an imaging device

Abstract

An imaging device includes a photoconductive drum charged by a charge roll and opposed by a transfer roll to transfer an image from the drum. The drum becomes biased to a negative voltage by setting charges of negative voltage on both the charge roll and transfer roll. A controller switches the bias of the transfer roll to a positive voltage from the negative voltage and a delta or difference in a charge of the drum is determined from before and after the switching. Based on the delta, the voltage on the charge roll is boosted by a boost voltage to improve the charge on the drum. In this way, deteriorating or defective charge rolls can be still used to charge the drum to a proper voltage for imaging. Techniques for determining the delta, the boost and the magnitude of voltage charges are further embodiments.

The invention claimed is: 
     
       1. An imaging device, comprising:
 a photoconductive drum for hosting a latent image that becomes developed with toner to create a toned image; 
 a charge roll opposed to the photoconductive drum for charging the photoconductive drum to a voltage that is discharged by a laser beam to create the latent image; 
 a transfer roll for transferring the toned image from the photoconductive drum to a sheet of media; 
 a high-voltage power supply; and 
 a controller to coordinate with the power supply to set a charge on the charge roll for said charging the photoconductive drum and to determine whether or not the charge roll is defective or has become deficient over time and, if so, the controller being configured to add a boost voltage to the charge roll to improve the charge on the photoconductive drum for imaging, wherein the controller is further configured to set a charge on the transfer roll and switch a polarity of the charge on the transfer roll when determining said whether or not the charge roll is defective or has become deficient over time. 
 
     
     
       2. The imaging device of  claim 1 , wherein the controller is configured to bias the drum to a negative voltage by setting a negative voltage charge on the charge roll and setting a negative voltage charge on the transfer roll and to said switch the polarity by setting a positive voltage charge on the transfer roll. 
     
     
       3. The imaging device of  claim 2 , wherein the positive voltage charge on the transfer roll exists in a range from +500 Vdc to +4500 Vdc inclusive. 
     
     
       4. The imaging device of  claim 3 , wherein the positive voltage charge on the transfer roll is about +2500 Vdc. 
     
     
       5. The imaging device of  claim 1 , further including a resistor connected to the transfer roll from ground, the controller configured to read a current through the resistor. 
     
     
       6. The imaging device of  claim 1 , further including a laser having a laser power, the controller configured to boost the laser power if the charge roll is said defective or has become deficient over time. 
     
     
       7. The imaging device of  claim 1 , wherein the charge roll is −1200 Vdc. 
     
     
       8. The imaging device of  claim 1 , further including memory accessible by the controller for storing the boost voltage, wherein the boost voltage exists in a range 0 to 150 Vdc. 
     
     
       9. The imaging device of  claim 1 , further including a weather station connected to the controller to supply to the controller an operating temperature and relative humidity. 
     
     
       10. The imaging device of  claim 1 , further including a weather station connected to the controller to supply to the controller an operating temperature and relative humidity. 
     
     
       11. An imaging device, comprising:
 a photoconductive drum for hosting a latent image that becomes developed with toner to create a toned image; 
 a charge roll opposed to the photoconductive drum for charging the photoconductive drum to a voltage that is discharged by a laser beam to create the latent image; 
 a transfer roll opposed to the photoconductive drum for transferring the toned image from the photoconductive drum to a sheet of media, the transfer roll connected to ground through a resistor; 
 a high-voltage power supply; and 
 a controller to coordinate with the power supply to set a charge on the charge roll for said charging the photoconductive drum and to determine whether or not the charge roll is defective or has become deficient over time and, if so, being configured to add a boost voltage to the charge roll to improve the charge on the photoconductive drum for imaging, the controller further configured to bias the drum to a negative voltage by setting a negative voltage charge on the charge roll and setting a negative voltage charge on the transfer roll and switching the polarity of the transfer roll by setting a positive voltage charge on the transfer roll and sensing before and after the switching a current through the resistor connected to the transfer roll. 
 
     
     
       12. The imaging device of  claim 11 , further including a memory accessible by the controller for storing the boost voltage. 
     
     
       13. The imaging device of  claim 11 , further including a laser having a laser power, the controller configured to boost the laser power if the charge roll is said defective or has become deficient over time.